It's nice and warm in dress uniform (3)

I believe the answer is:

sun

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'it's nice and warm' is the definition.
I can't tell whether this definition defines the answer.

'in dress uniform' is the wordplay.
'in' indicates a hidden word.
'SUN' can be found hidden inside 'dress uniform'.

Can you help me to learn more?

(Other definitions for sun that I've seen before include "Louis XIV of France was known as The . . . King" , "Rag" , "Warmer" , "It's sol in Latin" , "Earth's nearest star" .)

I've seen this clue in the Evening Standard.

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